1. Field of Invention
The present invention relates generally to automated manual transmissions and, more particularly, to an automated manual transmission which optimizes the realization of a first-speed gear ratio.
2. Description of Related Art
Generally, transmissions for vehicles are classified into manual transmissions (MTs) and automatic transmissions (ATs).
Automatic transmissions are operated in such a way that rotational torque and speed are automatically changed. Typically, the flow of fluid is used in interrupting power or increasing the torque. Such an automatic transmission automatically shifts gears in a predetermined gear shifting pattern depending both on the speed of a vehicle and on the degree by which an accelerator pedal is pressed.
Manual transmissions are operated in such a way that a driver manually shifts gears. To shift gears, a clutch separates a shift actuator from an engine. In this state, gears are shifted. After gear shifting is completed, power is transmitted again through the clutch.
Meanwhile, to improve manual transmissions, automated manual transmissions (AMTs) in which a clutch and a gearshift lever are automatically manipulated have been developed and are in use.
Such automated manual transmissions use the structure of a typical manual transmission as it is and automatically control the clutch and the gearshift lever using a hydraulic control unit. Therefore, automated manual transmissions can be called next generation transmissions that have not only the advantages of manual transmissions, which can provide high fuel efficiency and are relatively inexpensive, but also the advantages of automatic transmissions, which can facilitate shifting of gears.
In automated manual transmissions, a clutch interrupts power during a process of shifting gears. Given this, automated manual transmissions are problematic in that the shift quality deteriorates while power is interrupted.
Particularly, the above problem becomes more obvious when a vehicle moves at a low speed than when it moves at a high speed. Recently, to overcome the above problem, improved automated manual transmissions using two clutches have been proposed.
As shown in FIGS. 1 and 2, an automated manual transmission using two clutches is designed in such a way that: a first clutch C1 and a second clutch C2 are connected to each other by a hollow input shaft I; and power to the first-speed gear, third to seventh-speed gears and R (reverse) gear is obtained using power transmitted from the first clutch C1, and power to the second-speed gear is obtained from the second clutch C2.
The automated manual transmission using two clutches requires two synchronizers S1 and S2. A first output shaft 01 and a second output shaft 02 are placed out of a center line of the input shaft I and a differential gear DG. Hence, there is a problem in that the distance between the input shaft I and the output shafts 01 and 02 and the distance between the output shafts 01 and 02 and a central shaft of the differential gear DG are increased.
Furthermore, when the hollow input shaft I is used, the size of a first-speed drive gear D1 is increased. To form a suitable gear ratio, the size of a first-speed shift gear G1 must also be increased. The distances between the shafts are further increased. An increase in the size of the gears increases the weight of the entire transmission.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.